Switches comprise backside ports and frontside ports. Backside ports are used to, for example, connect one switch to another switch to form a stacked switch. Backside ports typically have a maximum link distance of five meters or less, but communicate at a very high speed to allow multiple switches to communicate and act as a single larger switch. Frontside ports are ports used to typically attach devices to the switch. The advantage of frontside Ethernet ports is that they can connect devices over long distances, but at a speed slower than the connection speeds of backside ports.
In the past, switches that were spaced far apart could be connected together in a ring using two of the frontside ports. As only two frontside ports were available for frontside stacking, ring topologies have been the only topologies available, making mesh and other interesting configurations impossible. In addition, prior switches could not support ports in an etherchannel that were distributed across the frontside stack because once a packet went across a frontside stack, the port identifier of the originating device was lost. Also, the prior architecture provided a filtering mechanism to drop frames going out a frontside stack port depending on its source, but this applied to all packets and no provisions were made for control packets which are meant for switch to switch communication.